The major project this year has been an analysis of the 20 year follow-up of the NHANES-I study of 1971-75. This randomized stratified sample of the U.S. Population is clearly the most representative population sample available. All-cause mortality has been related to the Body Mass Index in 4.949 men and women aged 55 to 74 years at entry. Adequate numbers of both African-American and Caucasian subjects could be analyzed since deaths in the 20 year follow-up ranged from 226 to 1265 subjects in the four race-sex groups. The mortality curves were invariably quadratic (mortality was fitted to BMI and BMI2). Diseases present at enrollment were classified into two groups: "A" diseases were those that could influence both body weight and mortality (for example, malignant neoplasms) and "B" diseases which are in the causal chain between obesity and mortality (for example, diabetes and hypertension). In addition, cigarette smoking was taken into account either by stratification into current, former, and never smokers or by adjustment for smoking status. Other potential confounders of the BMI-mortality association were also examined: socio-economic status (family income), physical activity status, and pattern of distribution of body fat (subscapular/triceps skinfold ratio). Thus this analysis took into account the most frequently noted defects of other studies of BMI and mortality. It also provides results on a random U.S. population, both men and women, black and white. The results showed that the hypothesized major defects of previous studies (failure to take disease and smoking into account, and inappropriately deleting diseases in the causal chain), upon testing, turn out to play almost no modifying role in this population. The BMI associated with minimal mortality is 25.6 kg/m2 in white men, 26.1 in white women, 27.1 in black men, and 29.7 in black women. These values, in 55-74 year old subjects support the Gerontology Research Center age-specific tables of 1985 and are not supportive of the 1995 Dietary Guidelines for Americans.